Project Summary/Abstract of Parent Grant: The aberrant production of low molecular weight aldehydes (i.e., formaldehyde and acetaldehyde) and lipid-derived aldehydes (e.g., 4-hydroxynonenal) have a major influence on the aging of stem cells. Molecular level changes that result from aldehyde-mediated epigenetic modifications, oxidative DNA damage and DNA cross-linking can lead to a variety of human diseases including autoimmune diseases, cancer, diabetes, and neurological disorders. However, our general understanding of the mechanistic underpinnings is insufficient owing to a dearth of methods to non-invasively detect reactive aldehydes, manipulate their subcellular concentrations, as well as to monitor the activity of aldehyde processing enzymes. The projects described in this application aim to address each of these three areas of research through the development of new chemical tools. Specifically, we will draw from our established expertise in molecular imaging and probe design to develop fluorescent and photoacoustic probes to non-invasively visualize endogenous aldehydes at the cellular and whole animal levels, respectively. We will complement this work by developing new aldehyde donors that can be employed to deliver a specific aldehyde species on demand using light. Since light can be focused with high precision onto small volumes within a cell, the delivery of a given reactive aldehyde can be achieved with unprecedented spatiotemporal control. Lastly, we will develop new fluorescent substrates to monitor the enzymatic activity of aldehyde processing enzymes implicated to play a crucial role in mediating stem cell plasticity. This work will be based on recent studies from our group where we have successfullydeveloped a new probe to detect stem cells via elevated aldehyde dehydrogenase 1A1 activity. The integrated approach in this proposed research spanning chemical synthesis to molecular imaging offers an exciting opportunity to study the biology of reactive aldehyde species related to aging and associated disease states.